Update: If you have Windows 10, this feature is built in, it’s called Night Light. If you open settings and search for it, you will find it. MacOS has this feature built-in, as well. On there, it’s called Night Shift.

F.lux is great.

It is the first piece of software I put on my machine after a clean OS install. It is an application that I use almost constantly, no matter what I’m doing on my PC. I tell other people about how great it is all the time, and once they try it, they all love it.

So, what does it do?

Let’s first get into color-temperature for a little bit, which is measured in Kelvin.

Basically, the higher the color-temperature is, the colder (and usually brighter) light looks. This chart gives a nice idea of what’s what.

Temperature

Source

1.850 K

Candle flame, sunrise/sunset

2.700–3.300 K

Lights in your house

5.000 K

Lights in offices

6.500 K

Daylight, overcast

6.500–10.500 K

Computer screens

15.000–27.000 K

Clear blue sky

Computer screens are designed to have the same color-temperature of daylight, which is fine during the day. The problem is, once the sun sets, daylight is way too bright and blue for your eyes to comfortably handle.

Anyone who owns a computer knows that sitting in front of it in the evening is tiring. It also keeps you awake. This isn’t strange, as you’re basically staring into bright daylight while the rest of the world around you is covered in soft, warm light (notice the difference in temperature between house lights and the computer screens in the chart).

F.lux fixes this. Once the sun sets outside, the sun sets in the color spectrum of your monitor as well.

This seems trivial, but it’s really not. You will be amazed at how much your computer screen normally strains your eyes after sunset once you get used to using F.lux.

Once active, it makes your monitor the same color temperature as your indoor lights: warm and easy on the eyes.

These two graphs illustrate the difference it makes in the overall spectrum. It’s quite dramatic.

f.lux turned off

f.lux turned on

It’s very much a “set and forget” application. You tell it where you are, and it will adapt to the sunset/sunrise of your location.

The only caveat: be sure to turn it off when you’re working on photos or graphics, because it obviously completely ruins your color accuracy. Surfing, office work, games, movies etc are all fair game.